The patella, commonly known as the kneecap, is a hard bone having an articular surface of cartilage on the posterior side. The articular surface is held in place against the femoral condyles by the patella tendon where it provides leverage that is necessary to a properly functioning knee joint. If the articular surface becomes damaged by trauma or by degeneration, proper knee functioning breaks down, often accompanied by joint pain and immobility. In such situations, a patella prosthesis, sometimes referred to as a button, may be inserted to restore normal functioning to the knee.
Patella prostheses have also been used in total knee replacement surgery to insure a reproducible interaction of a patella with the femoral and tibial portions of the total knee replacement. Usually in such procedures the posterior side of the patella is prepared, sized and reamed so that a patella implant, when fixed to the patella, restores the reconstructed patella to its natural or original thickness.
In one procedure, the patella is prepared for the patellar implant as follows. A patellar holding clamp is placed on the patella with a clamp ring on the posterior side. The patella is then reamed with a patella reamer to a predetermined depth. One method of determining when the reamer has reached the appropriate depth involves placing a guide member on the patellar holding clamp and a stop member on the reamer. The reamer is then urged toward the patella, guided by the guide member and the clamp ring until the stop member abuts the guide member. The patellar implant is then inserted into the prepared bed.
In known patella reamers, a patella cutting surface is mounted onto a tool driver, which in turn is mounted in the chuck or collet of a portable drill or flexible powered shaft. Patella cutting surfaces are separable from their tool drivers in order to replace or sharpen the cutting edges as they are used. Tool drivers are relatively expensive, and thus must be cleaned and reused.
Some previous tool drivers grip the cutting surface by means of a flange and slot and a spring loaded ball catch or other catch devices. In some situations, the catch can trap dried blood and other debris, which can be difficult to remove during cleaning. Further, unless the tolerances of cutting surfaces and tool drivers are made very close, there can be considerable free play between the cutting surface and the tool driver. This increases wear and decreases the precision of the tool.
Additionally, because the manufacturing cost of producing these sophisticated cutting surfaces is too high for them to be disposable, the cutting surfaces being reused must be removed, cleaned, and sharpened. There is also an accompanying cost of making the cutting surface aseptic for each operation.
A patella cutting system with a disposable cutting lid is disclosed in U.S. Pat. No. 5,295,992. This patella cutting system employs a cutting lid that is secured to the tool driver by means of pins on the tool driver and slots on the cutting lid. This patella cutting system leaves a planar reamed surface in the patella and the cutting system stores cut bone debris within the tool driver behind the cutting lid. This system has disadvantages however, including difficulty in gripping the smooth surfaces of the cutting lid in order to lock or unlock the lid in a surgical setting where the surgeon is wearing gloves that are often coated with bodily or other fluids. In addition, storing bone cutting debris within the tool can lead to an increased need to remove of the cutting lid during surgery as the tool may fill up with debris. A similar cutting lid, referred to as a patellar basket, is described in U.S. Pat. No. 5,536,271.
Despite existing technology, there remains a need for a disposable cutting system useful within a patella reaming device.